A gas burner pilot is a device used to create a stable pilot flame by combustion of a low flow rate (relative to the main burner) gaseous fuel-air mixture. The pilot flame is used to ignite a larger main burner, or a difficult to ignite fuel. Gas pilot designs normally include an ignition system. One common type of ignition system used in gas burner pilots, as well as other burner systems such as flare systems, is a High-Energy Ignition (HEI) system.
HEI systems are used in industry for their ability to reliably ignite light or heavy fuels in cold, wet, dirty, contaminated igniter plug, or other adverse burner startup conditions. An HEI system typically utilizes a capacitive discharge exciter to pass large current pulses to a specialized spark (electric arc) igniter. These systems are typically characterized by capacitive storage energies in the range of 1 J to 20 J and the large current impulses generated are often greater than 1 kA. The spark igniter (also known as a spark plug, spark rod or igniter probe) of an HEI system is generally constructed using a cylindrical center electrode surrounded by an insulator and an outer conducting shell over the insulator such that, at the axially-facing sparking end of the spark rod, an annular ring air gap is formed on the surface of the insulator between the center electrode and the outer conducting shell. At this air gap, also called a spark gap, an HEI spark can pass current between the center electrode and outer conducting shell. Often a semiconductor material is applied to the insulating material at this gap to facilitate sparking. In general, the spark energy of an HEI system is significantly greater than the required Minimum Ignition Energy of a given fuel, given that the appropriate fuel to air ratio and mix present. This extra energy allows the ignition system to create powerful sparks which will be minimally affected by the adverse burner startup conditions mentioned above.
For cost and size considerations it is desirable to minimize the output energy of an HEI system, however, as output energy is decreased it becomes increasingly more difficult to create sparks in adverse burner startup conditions.